The private security force in Arkham City is TYGER Security. It is a rogue private military organization placed in charge of monitoring the prison city and enforcing Hugo Strange’s authority.
TYGER troops patrol the walls, operate checkpoints, arrest new prisoners, and control the city’s surveillance and security systems. Unlike the inmates’ rival gangs, TYGER is an organized force with military training, armored equipment, helicopters, and strict orders. Its personnel treat Arkham City as a containment operation rather than a conventional prison.
The organization works for Hugo Strange and Quincy Sharp, the officials behind the open-air prison project. When Bruce Wayne publicly opposes Arkham City, TYGER soldiers arrest and imprison him there, demonstrating that the force serves the project’s political leadership as much as public safety.
A common mix-up is calling them the Militia. The militia is associated primarily with the Arkham Knight and his occupation of Gotham in Arkham Knight. In Arkham City, the guards enforcing Protocol 10 are TYGER Security, usually styled in the game as “TYGER.”